My new Chennic dc-dc unit was showing some voltage sag when the vacuum pump kicked in... noticible only at night when I had headlights going. It caused a momentary headlight 'blink', and was enough to make the radio blink as well! I looked at the capacitors that the stereo guys use, but they are pretty big and expensive. I ended up finding a very small (1.3aH) 12v sealed lead battery for less than $20, and just put this in as an auxilary battery. My dc-dc is 'always on', so it should keep the little battery up, and the battery can pick up the slack when the vacuum pump or any other 12v load causes a momentary voltage sag. NOTE: this works pretty well unless I have 'everything on'; headlights, heater, and vacuum pump kicks in. Without heater its ok. I'm looking for a way to 'soften the start' on the vacuum pump....